BlackBerry's co-founders, Mike Lazaridis and Doug Fregin, are working with advisors to explore buying all or part of the ailing BlackBerry, according to a U.S. Securities and Exchange Commission filing.

The Schedule 13 D filing, posted online Thursday, says that the two men have agreed to work exclusively with each other "with respect to any potential acquisition of all or a part" of BlackBerry.

They jointly own nearly 8% of BlackBerry, or about 41.6 million of the 524 million common shares that BlackBerry reported it owned in March.

Their 8% compares to the 10% owned by Prem Watsa, head of Fairfax Financial Holdings of Toronto. Fairfax has struck a preliminary deal with BlackBerry to buy BlackBerry for $4.7 billion and take it private.

Lazaridis and Fregin have hired Goldman, Sachs & Co. and Centerview Partners "to assist with their review of strategic alternatives with respect to the shares," the filing states. The filing also names Lazaridis and Fregin as legal representatives of investment holding companies under the names of Ontario Inc. and Ontario Ltd. that are party to the agreement to explore buying BlackBerry.

Lazaridis and Fregin are officially listed as retired in the filing, but also recently co-founded Quantum Valley Investments, a venture fund.

BlackBerry was founded in 1984 and Lazaridis served in various roles as president, co-CEO and co-chairman in subsequent years. Fregin formerly served as vice president of operations. In 2011, Lazaridis stepped down as co-CEO of BlackBerry along with then co-CEO Jim Balsillie; both were replaced by current CEO Thorsten Heins. Lazaridis stayed on as vice chairman at BlackBerry until earlier this year.

The news of the interest in BlackBerry by Lazaridis and Fregin comes after months of uncertainty for the company. BlackBerry recently reported a Q3 loss of nearly $1 billion, attributed mostly to slack sales of the Z10 smartphone and the planned layoff of 4,500 workers of a total force of 12,500.

Analysts have said the smartphone business at BlackBerry is essentially worthless, and that it could cost up to $2 billion to shut that portion of the company down. Meanwhile, the secure network is valued at up to $4.5 billion and BlackBerry 'spatents might be worth $3 billion. BlackBerry has more than $3 billion in cash and investments as well.

Reaction to the news Lazaridis might buy BlackBerry brought some derision. "Wouldn't that be a bit like Tom Landry coming back to coach the Dallas Cowboys? He won two Super Bowls, but the last few years with him at the helm were pretty ugly," said Bill Menezes, an analyst at Gartner.